The present invention relates to a method of producing tubular wrappings.
In particular, the present invention relates to a method which may be employed to advantage on cigarette packing machines for producing the tubular outer wrapping, preferably but not necessarily parallelepiped or similar in shape, or the tubular transparent wrapping of so-called "soft" packs.
On known packing machines, the above tubular wrappings are normally produced by successively feeding sheets of wrapping material over respective openings formed on the periphery of a wrapping wheel and each defining the access to a respective radial seat on the wheel. The wrapping wheel is jogged about its axis so as to successively feed said seats to a loading station where each seat is stopped long enough to receive the unwrapped product. Insertion of the product inside the seat usually results in simultaneous insertion of the respective sheet of wrapping material, which gradually folds in a U about the product as this is fed inside the seat. The length of the wrapping material is normally such that, when the product is fully inserted, the opposite end portions of the sheet project outwards of the seat.
The loading station usually presents a first folding device which, after the product is inserted and before starting up the wrapping wheel again, is activated for folding a first of said end portions, usually the one upstream in relation to the traveling direction of the seat, on to the product. The wrapping wheel is then jogged forward one step to feed the next seat into the loading station and the foregoing seat beneath a fixed outer plate, which engages the second of said end portions and folds it backwards on to the product, at least partially overlapping the first end portion. For one or more successive steps of the wrapping wheel, the product, with the end portions of the wrapping material folded as described above, slides underneath the fixed outer plate, which provides for holding the end portions of the wrapping material in the downfolded overlapping position.
This continues until the product is arrested on the wrapping wheel at a joining station where the fixed outer plate ends and the product is arrested in such a position as to partially project beyond the end of the fixed outer plate, but with a sufficiently large portion still engaged by the plate for securing the end portions of the wrapping material in the downfolded overlapping position. At this point, an external joining device, e.g. a gumming or welding device at the joining station, is activated for joining the portion of the two end portions of wrapping material projecting beyond the fixed plate, so as to product said tubular wrapping.
The above method of producing said tubular wrappings therefore requires the use of a jog feed device, in this case the wrapping wheel, for at least enabling the product to be arrested for operating the joining device.